Keyed oscillator circuit



Jan. 17, 195 0 H. F. MAYER 2,495,115

KEYED OSCILLATQR CIRCUIT Filed Nov. 30, 1943 5 Shee'ts-Sheet l TRIGGER AMP.

Inventor: Harry F. Mayer, by J His Attorngy.

Jan. 17, 1950 H. F. MAYER 1 KEYED OSCILLATOR CiRCUIT Filed Nov. 30, 1.943 3 Sheets-Sheet 2 A] I F 2..

I TRANS EEP c PPE TRIGGER 3 Mv. TIMINGMV. ZMR PULSER I I l5 17 & B

I SWEEP l/ l/ 1 Jan. 17, 1950 H. F. MAYER 2,495,115

' KEYED OSCILLATOR cmcurr Filed Nov. so, 1945 3 Sheets-Sheet 5 Fig.4.

54 v Y Y tss Invent-or": W Harry FiMayev,

58 b w Z y His ttor-ney.

Patented Jan. 17, 1950 2,495,115 KEYED osoILLA'roa CIRCUIT Harry F. Mayer, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November so, 1943, Serial No. 512,301

3 Claims. (01. 250-36) The present invention relates to radio locating equipment for determining the range of remote objects by the time of travel of pulses of radio waves and is particularly concerned with circuits jects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1 and 2 are circuit diagrams of equipment embodying my invention and Figs. 3 and 4 are explanatory diagrams illustrating the operation.

Referring to Fig. 1 of the drawings, there is shown radio locating equipment having a directional antenna 1 connected to a transmitter 2 keyed by a pulser 3 to transmit directional pulses of radio waves at the desired repetition rate. The antenna is also connected to a receiver 4 through a TR box 5 which limits the amplitude of the pulses appearing at the antenna in such a manner as to prevent injury to the receiver by the transmitted pulses and without offering any substantial resistance to the echoes of the transmitted pulses. The receiver output is fed through a switch 6 and a pulse amplifier l to the center electrode 8 of a circular sweep cathode ray tube 9 having a beam deflected in a circular path by A. C. sweep voltages 90 degrees out of phase applied respectively to the vertical and horizontal deflection plates l0 and l I in a manner hereinafter described. The receiver output which consists of transmitted pulses and echoes arriving after intervals corresponding to the range of the reflecting objects causes radial deflections of the beam which appear on the cathode ray tube viewing screen at 12 and IS. The range of the reflecting objects can be determined by angular distance between the deflection l2 corresponding to the transmitted pulses and the deflections l3 corresponding to the echoes.

It is obvious that the accuracy of the range determination is directly dependent upon the accuracy with which the frequency of oscillation is maintained and relative amplitudes of the sweep voltages applied to the deflection plates and l 1. Furthermore, the sweep voltages should be syn- 12) will remainfixed on the cathode ray tube viewing screen. This is'essential not only for determining the range of the reflecting objects but also for distinguishing the echoes from the nonsynchronous noise voltages causing the erratic deflection's Hi intermediate the deflections l2 and I3.- It isalso desirable that the pulse frequency oithe transmitter be variable independent of the sweep frequency so as to prevent synchronous interference due to simultaneous operation of more than one equipment in the same locality.

In the present equipment the independent adjustments are obtained by using a pulse frequency multivibrator [5 to initiate the pulse transmission and the generation of the sweep voltages. Because the multivibrator is utilized to initiate these operations the pulse frequency and the frequency of the sweep voltages can be independently varied. The leading edge of the pulse frequency multivibrator output, shown in line A of Fig. 3,

. fires a delay multivibrator l6 having an output shown in line D of Fig. 3. The trailing edge of the positive pulses produced by the delay multivibrator fires a sweep timing multivibrator ll having an output shown in line E of Fig. 3. The sweep' timing multivibrator output is amplified and clipped in a clipper amplifier l8 to convert the output to a square-wave form indicated in line F of Fig. 3 and is then fed through a trigger amplifier [9 having an output indicated in line G of 1 Fig. 3 with a sharp leading edge for firing the pulser 3'so that the transmitted pulses, indicated at Illa in line H of Fig. 3, occur precisely at the leading edge of the sweep timing multivibrator output. As is apparent from Fig. 3, the time interval between the leading edge of the pulse frequency multivibrator output and the transmission of a pulse of radio waves is equal to the delay interval of the delay multivibrator Hi. If more than one equipment is to be used in the same locality, interference can be'prevented by adjustment of the delay intervals of the respective equipments, provided the delay interval is at least as long as one cycle of the sweepfrequency. For example, another equipment might have its delay multivibrator set to turn its sweep timing multivibrator on at the trailing edge of the output pulse of the sweep timing multivibrator of the present equipment.

Interference may also be avoided by externally synchronizing the pulse frequency multivibrator IS with a sine wave, each equipment being supplied with a difierent phase voltage of the same sine wave synchronizing signal.

The sweep voltage is obtained from an oscillator having a resonant circuit consisting of an inductance 20 and a variable condenser 2| coupled to a discharge device 22, the amplitude of the oscillations being adjustedrby a slider23 on a cathode resistor 24. The resonant circuitvof theioscillator is tuned to a frequency such that the period of one complete oscillation is equal to the:...-'.

7 period of the Sweep timing multivibrator output. The oscillator output is taken from oppositesides of the grounded center point ofi-theeinductance 20 and fed through a push-pullxamplifiersfla; 24b. to the vertical plates ID of the cathode ray tube.

The horizontal plates H on theicathoderay-tubee.

are fed from a similar push-'pull'amplifier 24c; 25

4 line H of Fig. 3, accordingly appear on a circular sweep trace on the viewing screen of the cathode ray tube spaced apart in accordance with the range of the reflecting objects.

Since the accuracy of the range determination depends upon the frequency of the sweep oscillater, it is desirable that the frequency of the sweep: oscillator be readily calibrated. This is effected byopening the switch 6 to disconnect the receiver 1 and by closing switches 33, 34, 35,

43521 which respectively connect a crystal oscillator, 36. t0. the pulse amplifier 1, short circuit the pulsefrequen'cy multivibrator l5, connect the grid 30ofthe device 29 to a source of negative connected to the oscillator output through-res 1 sistance-capacitance phase shifting networks 26,

2-1 which effect -a-90.-:degree. phase shiftrin the:vo1t age, fed to the horizontal plates; Because the, voltages applied; to; the horizontal. andzvertical plates are displaced .90.,deg -rees intime phase, the: beam ofthe-cathode ray;tube.-is:deflected inrazcir cular-trace-if theamplitudes. of the.respective voltages are made equal by adjustingsliders- 28 at:

the inputs of,;thepush-pull:-amplifiers:

The. sweep oscillator :issyncl'ironized with; the;-

transrnitted pulses. by a device 29':- connected to:: ground through a branch icircuit. including;- part: of the. inductance 20nandnormally; biased; sons. to carry suificientzcurrent tosdamp oscillation in-v the sweep oscillator- Thefdevice-29i-isacontrolled,;

by applying to its grid 30*arnegatiye-pulseafrom; the pulse. frequency multivibrator .l -(a mirror image; of the positive.-pulse indicated in liner-A-t of Fig. 3) which biases-thedevice: 29-toecut'-0ff,-. The interruption of; current throughwthe. device-. 29 causes an :induced voltagezin; the inductance: 2|] which starts an oscillation in the-resonanticirs cuit of .the sweep osoillatorwhich: is-acontinuedat the level determined by the adjustmentofi-the r slider 23 onv the cathode. resistor 24'... TheI'OsCilr" lator, output, as. indicated in -line B 0t: Fig.1. 3'; starts at the 1 leading edge of; the output pulse of? the pulsefrequency'multivibrator I and continues}:

at constant amplitude throughout-the output...

pulse. At the end of the outputpulse; the negatetive bias on thecgrid 30. isremoved and'thecur rent through the. device; 29 ;due,-t01itsinormal;bias:-

damps' the. sweeposcillationewithin a-.few.- cycles: Because. the sweep oscillation; is started. by a transient: clue'to: the interruption ofyaacurrent, the; sweep oscillational-ways :starts inthe same mane ing. the. grid 3| of the cathode ray tubesbiased: 7

off during the. delay interval. of the delayr multi-i vibratorandbiasing ;thegridion. during-theisweem timing interval by connection to the outputof--. theclipper amplifiervlmj llhe transmi-tted .-pulses bias.- potential; 3l. which biases the device 01f and permits continuousoscillation of the sweep oscillator, and connect the grid 3! to a positive bias voltage. A circular trace modulated by the crystal. oscillator frequency now appears on the cathode ray tube viewing screen as indicated at 38. The frequency of the sweep frequency oscillator is; adjusted .until the patternproduced by the: crystal oscil-latoris stationary; then the sweep. frequency is-an exact sub-multiple of the crystal.- freq-uency. Thediameter of the sweep trace can be adjusted by the-sliders 2'8 whichalso must.

be adjusted to causevoltages of equal amplitude onthe. horizontal and vertical deflection lates.

If these voltages are unequal, the sweep trace willbe an ellipsei-with themajor axis in line with the deflection plates to which the. greater. voltage is: applied. If the phase difference of the deflection voltagesis different from 90 degrees, the major axis of the sweep trace will be'inclined from the axeswo-f the-deflection plates. This results-in a diagonal ell-iptici-ty which iscorrectedby adjusting the resistances-of networks 26 and 21. The- -concentricityof 1 the sweep trace is adjusted by centering voltages (notshown) applied to. the; deflection. plates. This-adjustment can be quickly. made at any time by moving the switchesto the".

calibrate position- After calibration, the

equipmentv isfreturned to operation by opening.v the-switches-33, .34, 35aand closing the switch:- 6; Thereq-uipmentis now in the-operating posi t ion"and the-length of the sweep trace may be. adjusted by adjustingthe sweep timing multi. vibratorso. the sweep timing interval is equal; to-360 degreesvof. the sweep. frequency, i. e., so

the; sweep; trace. is a-full circle.

In Fig. 2. is shown locatingv equipment difieringwfrom thatpreviouslydescribed in: the use-oh ahorizontal instead of -a:- circular sweep. for. therange scale and in themanner of calibrating the). range -scale.-. Corresponding partsare indicated...

by; the sameareference numerals.

. Thasweep voltage isderived from a-saw-tooth. sweep'circuit. 39'rfed from the clipper amplifierlih'and. supplying tocthe horizontal. deflection-Q plates; l'l .ofthe cathode raytubea-voltage which: increases linearly during; each sweep timing in tervalsandzabruptly decreasesat the. end of each sweep.-timing=interva1. The receiver output is ap: plied-through the switcht to the vertical. de-' fleetion: plates. l9. causing thedeflections I2 and-- l3-respectively corresponding to the transmitted. pulses-and the echoes and spaced in accordance:

with the range: of the reflecting objects.

The range scale is calibrated by anoscilla-tor,

ductance 46: anda. condenser 4L coupled toa. deviceiil'inisuch a manner-as to sustain oscilla-i The inductance. in serieswithwdevice 43 (corresponding;to:- andthe; echoes, one.of;which.-is-,;shawrrrats32-om device 29am Fig. 1:) having a grid Mhnormallyg;

tions-of a constant amplitude. is:

biased so as to cause a unidirectional flow of current through the inductance 49 of sufficient magnitude to damp oscillations. When the device 43 is conducting, a unidirectional current flows through the device 42. During the sweep timing interval, the device 43 is biased to cut-off by a negative voltage from the sweep timing multivibrator, the negative voltage being mirror image of the voltage fed to the clipper amplifier 18. The interruption of the current through the device 43 at the beginning of the sweep timing interval starts a transient oscillation in th resonant circuit 49, 4| which is maintained at the starting level by the device 42. The oscillation level is adjustable by a slider 45 controlling the bias of screen grid 46. At the end of the sweep timing interval, the removal of the cut-01f bias on the grid 44 causes a resumption of the flow of current through the device 43 to quickly damp the oscillations in the resonant circuit 40, 4|. The output of the oscillator is taken from a load resistor 91 and fed to the grid 48 of a device 49 which functions as a clipper amplifier. In this device the negative halves of the sinusoidal voltage appearing at the load resistor 41 are clipped to a square wave shape which is differentiated by the inductance 50 and resistance 5| and by the condenser 52 and resistance 53 to produce positive and negative peaks 54, 55 coincident with the zero and l80-degree points of the oscillator output. The differentiated voltages are applied to the grid 56 of a device 57 connected as a clipper amplifier. The negative peaks 55 have no effect, but the positive peaks 54 are clipped and amplified causing negative pulse voltages 58 at the load resistor 59. The pulse voltages 58 occur at the beginning of each cycle of oscillation of the oscillator 49, ll, 42, the first pulse occurring coincident with the negative voltage applied to the grid 44 at the beginning of the sweep timing interval. Since the oscillator frequency is known the pulses 58 provide a time scale.

The pulses 58 are used to calibrate the range scale of the equipment by opening the switch 6 and closing the switch on a contact 69 connected to the load resistor 59. This causes deflections 6! on the sweep trace of the cathode ray tube spaced apart from left to right at intervals equal to the period of the oscillator, the first deflection being coincident with the transmitted pulses. Since the time of travel of the pulses of radio waves to and from a reflecting object is a measure of its range, the deflections El provide a range scale.

In both forms of the invention, the sweep oscillators (29, 2! of Fig. l, 49, 4! of Fig. 2) start oscillation synchronous with the keying impulses and without any transients. In each oscillator the transients are eliminated by having the keying device (38 of Fig. 1, 48 of Fig. 2) cause the inductance and condenser of the oscillator circuit to have a current and charge prior to the keying impulse corresponding exactly to some part of the cycle of the steady state oscillation. At the instant of interruption of the current through the keying devices, the resonant circuits of the oscillators are at steady state conditions and the subsequent oscillations build up without any transients. tube control circuit is described, illustrated and claimed in my copending application Serial No. 569,740, filed December 26, 1944, now matured into Patent No. 2,457,580 and assigned to the same assignee as the present invention.

The above-described cathode ray While I have shown particular embodiments of my invention, it will be understood that many modifications may be made without departing from the spirit thereof, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim and desired to secure by Letters Patent of the United States is:

1. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, another discharge device having at least a portion of said inductance in the cathode circuit thereof, said other discharge device normally presenting an impedance sufilcient to provide rapid damping of said oscillations and carrying a unidirectional current sufficient to establish an energy level in said inductance equal to the peak energy level appearing therein resulting from said oscillations, and means for cyclically keying said other device oiT whereby oscillations start in said circuit at said peak energy level.

2. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, another discharge device having at least a portion of said inductance in the cathode circuit thereof, said other discharge device normally presenting an impedance sufficient to provide rapid damping of said oscillations and carrying a unidirectional current suiiicient to establish an energy level in said inductance equal to the peak energy level appearing therein resulting from said oscillations, and means for cyclically keying said other device off whereby oscillations start in said circuit at said peak energy level, said devices being connected to a common source of positive operating potential.

3. In a keyed oscillator the combination of a resonant circuit including an inductance, a first discharge device connected to said resonant circuit so as to sustain oscillations therein, a second discharge device having at least a portion of said inductance in the cathode circuit thereof, means for applying a keying wave having alternate positive and negative portions to a control grid of said second discharge device, said second discharge device during said positive portions presenting an impedance sufficient to provide rapid damping of said oscillations and carrying a unidirectional current sufilcient to establish an energy level in said inductance equal to the peak energy level appearing in said inductance resulting from said oscillations, and said second discharge device during said negative portions of said keying wave being keyed on whereby oscillations start in said circuit at said peak energy level.

HARRY F. MAYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,362 Hansell Dec. 28, 1937 2,153,140 Diehl et al Apr. 4, 1939 2,181,568 Kotowski et al Nov. 28, 1939 2,189,549 I-Iershberger Feb. 6, 1940 2,227,598 Lyman et a1. Jan. 7, 1941 2,273,193 Heising Feb. 17, 1942 2,347,826 Heisner May 2, 1944 2,370,685 Rea Mar. 6, 1945 

